Permanent waving of the hair broadly involves two steps. The first step is the reducing step which involves an application of a reducing solution to hair to cleave S-S bonds of protein chains in the hair. The second step is the oxidation step which involves application of the oxidizing agent to restore the S-S-bonds in the new rearranged position. Wetting agents or other penetrants are normally employed to aid the reduction step. The efficiency of the reducing solution depends on pH, and the temperature employed, which may be up to about 60.degree. C.
The reducing step is generally carried out under alkaline conditions. The rearrangement of the S-S bonds results from both the mechanical stress put on the hair by the mandrels or waving rods and from the action of the alkali. The alkali serves to swell the hair by allowing the dissociated sulfur atoms generated by the cleavage of S-S bonds, to slip past one another more easily under the stress applied by the rods.
Under acid conditions the wave forming capacity of the reducing solution is drastically reduced making it necessary to apply heat to achieve a proper hair restructure.
In the oxidation step, the disulfide bonds are reformed in their new "curled" formations by an oxidizing agent such as bromic acid salts, perboric acid, hydrogen peroxide and the like.
There is a continuing effort to enhance the penetration of the reducing solution on the hair and accelerate the reducing step.
WO 90/03780 discloses the use of a reducing agent containing cysteine or its derivatives or cysteamine in combination with a mercapto compound selected from mercapto-ethanol, thiomalic acid, thiolactic acid and alpha-mercaptoethane sulfonic acid. Japanese Patent Application No. 57-62217 discloses the use of a reducing solution containing cysteamine hydrochloride in combination with a conventional reducing agent at a pH of about 9.
The reducing solutions of the prior art are generally inadequate for the production of a satisfactory curl, the durability of the curl over time, or in the clinical safety of the reducing agents.
It would be desirable to develop a reducing solution which provides a faster, more efficient curl at comfortable temperatures with minimum hair damage.